Two types of flight control exist on board aircraft:
primary controls which serve to control immediate movements; on an airplane these are generally flat surfaces situated in the trailing edges of the wings; PA1 secondary flight controls which serve to adjust the aerodynamic configuration of the aircraft to various stages of flight; this category includes wing slats and landing flaps and the rear tail plane. PA1 "Actionneurs--Des materiaux piezoelectriques pour les commandes du future" [Actuators--piezoelectric materials for future controls], Usine nouvelle, Oct. 31, 1996, No. 2568; and PA1 "Des commands de vol piezoelectriques" [Piezo-electric flight controls], Air et Cosmos/Aviation International, No. 1602, Feb. 28, 1997. PA1 continuous movements of small amplitude necessary for short-term piloting of an airplane (stabilization); these movements have a frequency spectrum that extends beyond the spectrum applicable to movements of the air-plane; and PA1 large-amplitude movements, that are much less frequent than the continuous movements and that are thus of very small spectrum width; these movements correspond to initializing major maneuvers of an aircraft, for example on an airplane, banking as is necessary for turning. PA1 "A new amplifier piezoelectric actuator for precise positioning and semi-passive damping", R. Le Letty, F. Claeyssen, G. Thomin, 2nd Space Microdynamics and Accurate Control Symposium, May 13-16, 1997, Toulouse. PA1 the control means comprise an electronic circuit controlling both of the motors as a function firstly of an external set point signal and secondly of signals output by two detectors, one providing information concerning the position of the control surface, and the other providing information concerning the relative angular position between the outlets of the two motors mounted in series; PA1 the motor is an actuator of the direct type and is controlled by a servo-control loop designed to maintain the position of the control surface on the flight set point; PA1 the control means apply speed control to the vibration motor as a function of the relative angle between the outlets of the two motors and in application of a non-linear control law; PA1 the control law is such that: PA1 the actuator further includes filter means at the outlet of the non-linear control; and PA1 the actuator comprises a plurality of vibration motors and a plurality of direct type motors in series.
In general, primary and secondary flight controls are implemented using hydraulic devices.
However, for various reasons (maintenance, pollution, fire risk, etc. . . . ), aircraft manufacturers are seeking to reduce the amount of hydraulics in control systems in favor of electrical controls.
An object of the invention is to propose a primary flight control of the electrical type.
Proposals have already been made for secondary flight controls to implement actuators by means of "vibration" motors, in which tangential and normal vibrations generated on a stator are transformed into continuous movement by the friction of the mechanical contact between said stator and the rotor.
For a general description of the use of that type of motor for secondary flight controls, reference can be made for example to the following:
It is known that primary controls must be capable of performing two types of movement:
Vibration motors could constitute advantageous candidates for primary controls since they are suitable for presenting high energy densities, they are capable of withstanding high stresses, and they are capable of performing large-amplitude movements.
Nevertheless, with this type of motor, continuous movements of small amplitude lead to very rapid wear at the interface, such that these motors are of limited lifetime.
For secondary controls, proposals have already been made to use actuators that implement directly the displacement of piezoelectric, electrostrictive, or magnetostrictive materials, possibly with amplification, in order to achieve small-amplitude movement of the control surface.
Direct actuator structures of that type are described, for example in:
Nevertheless, even when amplified, such actuators do not provide amplitudes that are sufficient for primary flight controls.